Mechanical slip rings utilising direct contact electrical connections are still utilised in a large number of applications. These suffer from contact losses, contact failure and high maintenance costs.
Inductive Power transfer (IPT) systems have been developed which address these drawbacks. A basic problem that must be overcome in wireless power transfer system design is ensuring that power can be transferred between coil arrangements over sufficient displacements (i.e. between the primary side and secondary side), while maintaining sufficient power transfer.
Introducing magnetically permeable elements into either the transmitting coils or receiving coils can improve the performance of the system. Magnetically permeable elements increase the inductance of the transmitter or receiver coils. This means that less coil turns are required to achieve the same inductance value as a transmitter or receiver without magnetically permeable elements. Magnetically permeable elements can also be configured to ‘shape’ the magnetic field, which can be directed from the transmitter to the receiver. By directing the magnetic field, the coupling factor between the transmitter and receiver can be increased, thus improving the performance of the system.
Current IPT coil arrangements often suffer from a low magnetic coupling coefficient k, which results in limited power transfer capability, particularly for large air gaps, due to magnetic flux leakage between the limbs of the magnetically permeable cores. Decreased power transfer capability results in low efficiency, greater size and greater cost for a given power transfer capacity.
The physical space available for a wireless power transfer system is often limited, including in rotary applications for robotic joints and wind power pitch control. Further, a large air gap is often required for mechanical clearance. When the air gap is large, the magnetic flux tends to leak within the core limbs instead of linking to the other side, which can result in low magnetic field coupling.
It is an object of the invention to provide a magnetically permeable core and an inductive power transfer coil arrangement having improved magnetic coupling, or to at least provide the public with a useful choice.